The president of a country is not the same thing as a prime minister. A prime minister is part of a parliament, but a president is not. In some countries, (such as the United States or France), the president has more power and responsibility than anyone else. Such a president is often called the nation's chief executive. As chief executive, the president must take an active role in all phases of government. In other countries (such as the Republic of Ireland or Israel), to be president is more of an honor or a symbol, and the position has no real power. This kind of president is often called "head of state".

The American President is restricted by the written United States Constitution, which can be changed but only if two-thirds of Congress as well as the President and three-fourths of the states agree to it. The American constitution was created to make sure that the American executive never became as powerful as the British system it had broken away from. The British Prime Minister is part of both the Legislature and Executive, whereas the American President is the head of the Executive. The American governmental system shows a clear separation of powers unlike the British system.

All the president's ministerial appointments have to be vetted by Congress (Parliament) and Congress may have an opposition majority.

The president does not have the ability to introduce and influence legislation in the same way as the British prime minister.

Congress has much greater control over the budget and foreign policy than the British Parliament.

There are broad areas of American life, such as education, crime and punishment, over which the president has virtually no influence at all.